1. Field of the Invention
The present invention relates to a thin film electroluminescence element wherein a luminescent layer is sandwiched between electrodes. It specifically relates to a panel configuration for performing multicolored luminescence by superposing a plurality of substrates wherein thin film electroluminescence elements emitting light of different colors are formed respectively.
2. Description of the Prior Art
For a luminescent element used for a luminescent display, a surface light source or similar light source is utilized. An AC-driven-type high-brightness thin film electroluminescence element (hereinafter electroluminescence is referred to as EL) has been put to practical use in such a display wherein a thin film EL layer, with an active material added, is sandwiched between electrodes. The color of luminescence is determined by the kinds of material of the luminescence layer and the active material added thereto. For example, a yellow-orange luminescence is obtained by adding Mn into a ZnS film; a green luminescence is obtained by adding Tb thereto; and a red luminescence is obtained by adding Eu into a CaS film. In the case of a multicolored display being achieved by using these thin film EL elements, two systems are employed. That is, a system wherein elements having luminescent layers emitting light of different colors are formed on the same substrate and a further system wherein different substrates are used for each element emitting light of a different color (for example, refer to the U.S. Pat. No. 4,396,864).
FIG. 9 is a configuration diagram of a double-layer-structure thin film EL panel wherein conventional EL elements are formed on different substrates on a luminescence color basis.
Lower electrodes 2 and 12 configure matrix electrodes; lower insulating layers 3 and 13 are formed; and luminescent layers 4 and 14 emitting light of different colors are laminated sequentially on two sheets of top and bottom glass substrates 1 and 11; and further on the luminescent layers 4 and 14, upper insulating layers 5 and 15 and upper electrodes 6 and 16 are laminated in sequence. Each electrode of the matrix electrodes is connected to driving circuits A1, A2, B1 and B2 of independent power sources based on an electrode group basis. Each of the upper and lower thin film EL elements is driven to emit light independently in response to an application of voltage to each of the matrix electrodes.
In the case where elements having EL layers emitting light of different colors are formed on the same substrate, the color displaying apparatus can be fabricated, theoretically, by means of making the structure multi-layered. However, this brings forward problems of productivity, yield rate, reliability of the element and compounds as well as being practically difficult to fabricate. On the other hand, in the case where the EL elements are fabricated by using different substrates on a luminescence color basis, it is believed that this is promising but has not been technically studied. The present invention relates to the latter case, and proposes a solution for the problems of the cost and quality of display in practical use as described below.